In surgery in the region of an anatomical joint, such as during and after implantation of an artificial joint, care should be taken that the joint moves as freely as possible. For example, the joint should pivot and/or rotate without one joint component (artificially inserted as an implant) nudging or abutting another joint component during normal joint movement so as to jam when the joint is further moved. Such interference can lead to excessive wear and/or functional impairment of the joint.
According to known surgical methods, the condyles, as a precaution, should be trimmed anteriorly and posteriorly, as for example described in “The Oxford Phase 3, Unicompartmental Knee, Manual of the Surgical Procedure” published by Biomet Merck, “LCS Universal Kniesystem, OP-Technik” [LCS Universal Knee System, Operative Technique] published by DePuy, or “The M/G Unicompartmental Knee” published by Zimmer.
In order to detect an impingement, a method referred to as HIP ROM (range of motion) is known that can be implemented using a surgical navigation system, such as marketed by BrainLAB AG under the trade name Vector-Vision hip software. Marker arrays, for example, can be attached to each of the pelvis and the femur and can be tracked by a camera system. Then, after pivoting the hip joint about its center point, the coordinates of the pivoting point can be stored with respect to the pelvis and the femur. Since the hip joint can be regarded as a ball joint, during movement of the joint within its normal functional range, the two points coincide in the coordinate system of the camera. If, however, jamming occurs and a joint component is dislocated, for example, due to jamming, then these two points may deviate from each other. This deviation can be detected by software, although it is not possible to localize the jamming point or bearing point of the joints.
US 2005/0,113,720 A1, the contents of which is incorporated by reference in its entirety, discloses a method for determining the center point of rotation of a bone in a rotary joint, such as for example a femur in the ilium. DE 100 62 580 A1, which also is incorporated by reference in its entirety, discloses how the mechanical axis of a femur may be determined.
In general terms, the positions of joint components or bones can be detected, for example, by marker arrays or reference stars attached to the bones. The positions also can be detected by elements directly or indirectly connected to the bones, such as markers which can be localized, for example.